Ion implantation is a ballistic process used to introduce charged particle species (such as atoms or molecules, generally referred to as dopants) into a pre-chosen targeted workpiece substrate in order to make purposefully prepared articles having certain useful properties. In particular today, ion implantation is a manufacturing process used in the making of modern integrated circuits.
In most types of implantation systems, provision is made to move the workpiece to be implanted through the ion beam at a controlled velocity effective to achieve the correct dose of ions. In certain applications (particularly those using 300 mm wafers or larger sized substrates such as flat panel displays as the targeted workpiece for ion implantation), it is advantageous to generate ion beams in the form of ribbon-shaped beams having high aspect ratios, wherein the cross-sectional shape of the beam is much larger in one dimension than the other.
These high aspect ratio beams may be made either by scanning a smaller beam in one dimension at high frequency, or by forming a continuous ribbon-shaped beam. Once formed, such beams are commonly used in ion implanter apparatus and implantation systems where an individual workpiece (such as a silicon wafer or a flat panel display) is moved in a single dimension through the traveling ion beam. Typically, the larger dimension of the ion beam's cross section is greater than one dimension of the targeted workpiece undergoing ion implantation. Consequently, if the current density profile of the ion beam is sufficiently uniform, then as a result of one or more passes of the workpiece through the high aspect ratio ion beam, a uniform dose of ions can be implanted into the workpiece.
In such ion implantation applications, not only is it desirable that the ion beam profile be uniform, but it is also beneficial that the traveling beam have its ions moving in trajectories which are parallel to each other, and are under precise trajectory control—so as to present a uniform current density profile that is appropriate for the implantation of a uniform dose of ions at a constant and controlled incident angle into the targeted workpiece, (a semiconductor wafer or a flat glass panel). It is also very advantageous that the traveling ion beam be substantially free of undesirable charged species that may be concomitantly present within the ion source feed material and/or in the materials forming the ion source itself.